Production of fatty acid and fatty acid ester

ABSTRACT

The present invention concerns a process for forming a fatty acid, a fatty acid ester or a mixture thereof from a soap-comprising starting material, in which process a metal-ion forming agent is added to the starting material, whereby a mixture is formed, which contains an insoluble phase and a liquid phase, the insoluble phase is separated from the liquid phase, and an acid is added into the insoluble phase to form a fatty acid, or a monohydric alcohol and an acid catalyst are added to form a fatty acid ester, whereby two phases are formed, an aqueous phase and an organic phase, or, first, an acid is added and then a monohydric alcohol and an acid catalyst are added into at least a portion of the formed fatty acid to esterify the fatty acid.

The present invention concerns a process for forming a fatty acid, afatty acid ester or a mixture thereof from a starting materialcomprising soap, as well as use of the formed mixture.

BACKGROUND OF THE INVENTION

Biodiesel is mainly the methyl ester of fatty acids that is formedthrough the transesterification of long-chained fatty acids with analcohol (methanol). The fatty acid esters of natural fats consist mainlyof triglycerides, whereby a water-soluble glycerol that is unacceptableas biodiesel is released in the transesterification. Further, an alcohol(methanol) mixed into the aqueous glycerol solution and salts of fattyacids (later soap) are released in the process. This fraction containingglycerol, alcohol and soap still has, particularly with regard to thesoap, a high energy content. Theoretically, 10% by weight of glycerol isgenerated from the triglyceride. Depending on the process conditions,the proportion of the soap can vary greatly and rise up to tens ofpercent from the original total amount of triglyceride. Since the soapcompounds are dispersed and partly dissolved in the aqueous solution ofthe formed glycerol, their separation from the aqueous solution isdifficult. The soap disrupts the phase between the fat-soluble fattyacid esters and the water-soluble glycerol and tends to form differentdegrees of emulsions, creating a challenging problem in large-scaleprocesses with regard to separation techniques. Removal of the alcohol,such as methanol, would also require expensive vacuum distillation.Thus, it can be concluded, that manufacturing biodiesel using theafore-described method in modern technology is underutilization of themost energy-rich parts of the raw material. Purification of thecompounds generated in the process in order to increase their value ofuse is highly uneconomical already merely with regard to thepurification steps required.

To a great extent due to the aforementioned reasons, no cost-effectivesolutions for the utilization of the mixture of aqueous glycerol, soapand alcohol (methanol) have been found.

There are no business economically advantageous solutions fortransforming the multi-component mixtures containing glycerol as acomponent into commercial products. The significance of thistechnological deficiency is emphasized particularly as the interestgrows towards renewable sources of energy raw materials in addition tothe fossil raw materials.

BRIEF DESCRIPTION OF THE INVENTION

The present invention concerns a process for forming a fatty acid, afatty acid ester or a mixture thereof from a starting materialcomprising soap.

More specifically, the process according to the present invention ischaracterized by what is stated in the characterizing part of claim 1.

The use according to the invention, on the other hand, is characterizedby what is stated in claims 15 and 16.

The invention provides a new solution to a problem that relates to aprocess wherein esters of fatty acids are produced according to anestablished method using methanol or other short-chained alcohols fromglycerolipid-containing fat by treating them with alkali metalalkoxides. Glycerol and other alcohols as well as a water-soluble alkalimetal salt of fatty acids, soap, are formed in the process. The glyceroland the soap of the mixture decrease the utilization degree of the totalcarbon contained in the original fat used in the process and, thus, theeconomic efficiency of the process. An essential disadvantage of theutilization of the glycerol that is formed in the production ofbiodiesel, compared with pure glycerol, is the water, the soap and thetoxic methanol or other short-chained alcohol it contains as impurity.

It is known that the presence of soap in water and in a mixturecontaining water-insoluble oil prevents the separation of the aqueousand the oil phases from each other. In the aqueous solution of an impurepolyhydric alcohol, the soap disrupts the phase between the water andthe lipid formed from fatty acid esters so that separating the phasesbecomes complicated and, even at the best case, it contains water andother components that better dissolve in the aqueous phase.

An advantage of the invention is an integrated unit operation entity, bymeans of which an ester that is formed from ahydrocarbon-chain-containing fatty acid and short-chain alcohols can bereformed from a difficulty energy-economically utilizable impureglycerol minor flow, which is released from the transesterification oforganic fats. The apparatus used in the process is simple and thetechnology associated with it is known with regard the production andthe use. The process according to the invention is not bound toproduction scale, but it is readily scalable.

The invention enables, inter alia, the recovery of the energy-rich soapand the recycling into alcohol esters of fatty acids or free fattyacids. A process technical and economical advantage of the invention isthat, by means of it, the total utilization of the carbon of thefraction consisting of compounds that contain alcoholic groups andcontaining impurities can be solved for the manufacturing of fatty acidesters and fatty acids by a process that neither demands energyrequiring unit operations, such as heating, nor pressurized unitoperations and, which for functioning requires only the use of suchchemicals, which can be incorporated into the inner circulation of theprocess according to the invention.

Compared to the prior art, in every aspect the invention moreefficiently fulfils the principles of sustainable development byintensifying the total utilization of the raw materials and by thusdecreasing the need for using other raw materials. The process accordingto the invention consists of a functional entity having theprerequisites for updating the production costs of fatty acids andalcohol esters thereof to a level accepted by consumers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the main execution steps of the process according theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Since no profitable solutions have been found for the utilization of amixture comprising soap and a polyhydric alcohol and a monohydricalcohol, these components should somehow be separated from each other inorder to utilize said components separately.

We have found that soap can readily be precipitated apart from theglycerol-comprising oil-water-alcohol emulsion, the naturally separatingprecipitate be recovered and a methylation procedure be performed on theprecipitate, whereby finished biodiesel, i.e. a methyl ester of a fattyacid, is formed from the soap. Also other esters can be produced throughthe process. In this respect, the soap components of the impure glycerolfraction are already favorable as raw materials for biodiesel. Thus, thesoap can be separated almost quantitatively from the other components.The remaining glycerol solution, without the presence of soap, can beutilized separately.

Thus, the present invention concerns a process for forming a fatty acid,a fatty acid ester or a mixture thereof from a starting materialcomprising soap, preferably an alcohol and soap. The alcohol ispreferably methanol, ethanol, 1-propanol or a polyhydric alcohol, mostpreferably glycerol.

The term “soap” means a salt of a fatty acid.

Particularly, the present invention concerns a process, which comprisessteps, wherein a metal-ion forming agent is added to said startingmaterial to produce a mixture comprising an insoluble phase and a liquidphase. The insoluble phase is separated from the liquid phase and acidis added to the former. After separating the insoluble phase it ispreferred to repeat the addition of the precipitating ion-forming agentto the liquid phase and to treat the formed precipitate as above. Thisstep can be repeated until the formation of precipitate has essentiallydecreased. Acid is added to the combined insoluble phase to form fattyacid. The fatty acids are recovered and used as such or a monohydricalcohol and an acid catalyst are added to form fatty acid ester. Thus,two phases are formed, an aqueous phase and an organic phase. Thesephases are separated from each other and preferably both collected. Theorganic phase thus contains the fatty acid ester. Optionally, amonohydric alcohol and an acid are added to the insoluble phase withoutseparate recovery of the fatty acid, whereby an aqueous phase and anorganic phase is also formed, of which the organic phase contains thefatty acid ester.

Thus, the fatty acid can be used as such or a fatty acid ester, suitablefor biodiesel, can be formed therefrom using a monohydric short-chainedalcohol by treating the fatty acid with said alcohol. The proceduresrequired by the described process can be carried out by a person skilledin the art, and without complex apparatuses, likewise the requiredadditives (reagents) are known, safe and they have an established finalform of use.

Generally, the invention comprises a process based on mainly naturalsteps, by which a long-chained fatty acid or a fatty acid ester isproduced from an organic soap or mixtures thereof. In this context, theterm “long-chained” means a hydrocarbon chain of at least C₄, i.e. ahydrocarbon chain, having at least 4 carbon atoms. Preferably, thehydrocarbon chain has a length of C₁₀ to C₂₀, more preferably C₁₂ toC₂₀.

Thus, the process of the invention comprises the steps of:

-   -   transforming a water-soluble or dispersed soap formed from fatty        acids into the form of a water-insoluble soap by means of a        metal-ion forming agent, and    -   esterifying the water-insoluble soap formed from fatty acids        with an alcohol into an alcohol ester of fatty acids or        transforming it with an acid treatment into a free fatty acid.

According to a preferred embodiment of the invention, the methodcomprises the steps of

-   -   optionally adding acid, preferably an organic acid, more        preferably acetic acid, formic acid or lactic acid, to the        starting material to adjust the pH to a value of 3 to 8,        preferably to a value of 6 to 8,    -   adding a metal-ion forming agent, such as mineral salt of an        alkali earth metal, preferably an agent that forms Ca²⁺ or Mg²⁺,        more preferably calcium chloride or magnesium chloride, most        suitably calcium chloride, to the mixture as a solid or as an        aqueous solution, in an amount that precipitates at least 40% of        the soap, preferably in an amount, using which a stoichiometric        amount of metal-ion is formed with regard to the amount of soap,        most preferably a 5 to 10% by weight stoichiometric excess,        whereby an insoluble phase and a liquid phase are formed,        wherein the insoluble phase comprises the soap and the liquid        phase comprises the polyhydric alcohol, preferably glycerol, and        the monohydric alcohol, preferably methanol, ethanol or        1-propanol, most suitably methanol, or a mixture thereof,    -   separating the insoluble phase, where the soap has been        transformed into an insoluble soap, from the first liquid phase,        preferably by filtering or by decanting or by another procedure        generally used for recovering a precipitate,    -   adding an acid, preferably hydrochloric acid or sulphuric acid,        to the insoluble phase, whereby a fatty acid or a mixture of        fatty acids is formed,    -   optionally, the acid treatment can be carried out using a        mixture of an acid catalyst and an alcohol, where the acid        catalyst preferably is hydrochloric acid or sulphuric acid,        whereby an organic phase, which comprises a fatty acid ester or        a mixture of fatty acid esters, and an aqueous phase, which        comprises water and mineral salts, are formed, and    -   collecting the organic phase.

According to another preferred embodiment of the present invention, amixture, which is a fraction formed as a result of thetransesterification of a lipid, is used as a starting material in theprocess. According to a particularly preferred embodiment, the molaramount of the monohydric alcohol to be added to the fatty acid fractionwith regard to the molar amount of the organic matter is at least 40%,preferably an equivalent amount.

Particularly preferably, the invention contains the steps, wherein theoptional solid matter components are removed from the starting materialby filtering. After this, the acidity of the starting material isadjusted using a necessary amount of an acid, preferably acetic acid,formic acid or lactic acid, most suitably acetic acid.

The soluble soap present in the filtered starting material istransformed into an insoluble soap by adding a metal-ion forming agentto the mixture, preferably a mineral salt of a bivalent alkali earthmetal, more preferably a mineral salt of Ca²⁺, most preferably CaCl₂.Most suitably, the salt is added as a solid, whereby significant amountsof water can be avoided. The mixing time is controlled, until theformation of the precipitate has essentially stopped. When the solidshave been separated from the liquid phase, e.g. by filtering, a moist“soap cake” remains, which according to a particularly preferredembodiment is dried, after which mostly 5% by weight, preferably 0.1 to4% by weight, most suitably 0.1 to 2.5% by weight of water remains inthe precipitate.

The insoluble fraction (precipitate) formed is separated from the liquidfraction by filtering or by decanting or by other methods generally usedfor recovering a precipitate. An acid treatment is carried out for theinsoluble fraction, preferably by using hydrochloric acid as an aqueoussolution, most suitably in a concentration of 0.5 to 10%. Acid is addedin an amount that is sufficient to release the fatty acids.

According to a particularly preferred embodiment of the invention, theacid treatment and the esterification are carried out as an acidcatalyzed esterification or by gradually esterifying. Preferably, anHCl-methanol treatment is performed on the soap precipitate at atemperature exceeding the boiling point of methanol, more preferably atover 65° C., most suitably at 80° C. As a result of the treatment, atwo-phase mixture is formed, of which the second phase, i.e. the organicphase, is formed of methyl esters of a fatty acids, which are collected.It is preferred to add the phase containing the salt formed in theesterification into the starting material. Thus, the aqueous solutioncontaining mineral salts released in the esterification can be recycledto the step of mineral salt treatment of the soap.

The compounds that are added in the different steps of the process, suchas the bivalent alkali earth metal salts, such as CaCl₂ or the sidefractions formed by these, apart from NaCl, do not leave the processtotally, but they are preferably recycled internally in the process orthey form separate economically utilizable fractions and thus improvethe total economics of the process.

According to a particularly preferred embodiment of the presentinvention, the produced fatty acid is used for manufacturing alcoholesters of fatty acids. More preferably, these fatty acid esters and thefatty acid esters produced by means of the invention are used further inmanufacturing biofuels, such as biodiesel. Most conveniently, theproduct of the present invention is suitable as a feed in theesterification of fatty acids or in processes, where plant or animalbased lipids are hydrotreated, particularly as a feed in processes,where so called HVO (“hydrogenated vegetable oil”) is manufactured.

According to a preferred embodiment, the esters of the invention areused in manufacturing biodiesel or renewable diesel. Correspondingly,the fatty acids can be used for other fuels, analogous to diesel.

Correspondingly, the starting material used in the process of thepresent invention is preferably obtained, e.g. from themethanol-containing glycerol fraction generated in the manufacturing ofbiodiesel, which generally contains at least about 2 to 10% of soap.Since water causes the formation of soap in the transesterification, itspresence in the present invention is not detrimental, but in theaforementioned transesterification the amounts of water and a monohydricalcohol are minimized. Less than 20%, preferably 2 to 10%, of water isreleased into said methanol-containing glycerol fraction. This watercontent is preferred in the starting material used in the process of thepresent invention.

“Biodiesel” means, according to the EU-directive 2003/30/EY “amethyl-ester produced from vegetable or animal oil, of diesel quality tobe used as biofuel”. Thus, biodiesel consists of fatty acid esters.

On the other hand, with the term “renewable diesel” is meant ahydrotreated fat of an animal, a plant or a microbe, whereby “microbefat” means a fat that is derived from bacteria, yeast, mould, alga orother microorganism.

Both the fatty acids and the fatty acid esters formed in the inventioncan be utilized for the manufacturing of biofuels. They can be used assuch or they can be blended with other components, or the acid or esterstructures can be degraded using methods known in the art and the doublebonds can be saturated, whereby an n-paraffin product is obtained, whichon the other hand can be mixed into the other components.

EXAMPLES Example 1 The Manufacturing of Fatty Acid Esters

0.5 liters of the minor fraction containing glycerol and soap, generatedfrom biodiesel production using rapeseed oil, was measured and solidcalcium chloride was added therein under stirring until no moreprecipitate was formed (0.9 moles). The soap precipitate was separatedfrom the liquid glycerol fraction through filtering and was washed withwater, after which the precipitate was dried. Thus, 171 g of essentiallydry precipitate was obtained.

0.54 g of the obtained precipitate was weighed and 2 ml of a mixture ofmethanol and hydrochloric acid, wherein the portion of methanol was45.8% and the portion of acid was 54.2%, was added therein. The mixturewas heated in a closed container to 80° C. for one half hour and thefatty acid methyl esters (1 ml) were separated therefrom throughconventional separating procedures.

Example 2 The Manufacturing of Fatty Acids and their Esterification

The above obtained precipitate was treated with hydrochloric acid sothat the pH of the aqueous layer was permanently acidic (pH=2). Themixture was heated to 62° C. and the surface layer containing fattyacids was separated therefrom. The salts were removed from the layerthrough washing with water, after which the water remaining in the layerafter the wash as well as the water formed with the fatty acids wasremoved by drying using a dehydrating agent, whereby the fatty acidsremained.

11.4 g of the obtained fatty acid mixture was weighed and methanol (aquadruple molar amount) as well as HCl gas as a catalyst were addedtherein. The formed oil layer was washed with a methanol-water mixtureas well as with water until the washing water was neutral, after whichan oily ester layer (6 ml) was separated from the formed oil-solutionmixture.

Both the obtained fatty acid mixture and the corresponding fatty acidester mixture are well suited, for example, for the manufacturing ofdiesel fuels.

1. A process for forming a fatty acid, a fatty acid ester or a mixturethereof from a soap-containing starting material, characterized byadding a metal-ion forming agent is added into the starting material toproduce a mixture containing an insoluble phase and a liquid phase,separating the insoluble phase from the liquid phase, and adding an acidinto the insoluble phase to form a fatty acid, or adding a monohydricalcohol and an acid catalyst to form a fatty acid ester, whereby twophases are formed, an aqueous phase and an organic phase, or addingfirst an acid and then adding a monohydric alcohol and an acid catalystinto at least a portion of the formed fatty acid to esterify the fattyacid.
 2. The process according to claim 1, characterized in that thestarting material comprises, in addition to the soap, an alcohol, whichpreferably is a monohydric alcohol, most suitably methanol, ethanol,1-propanol, or a polyhydric alcohol, most suitably glycerol, or amixture of several alcohols.
 3. The process according to claim 1,characterized in that the starting material is a fraction formed as aresult of the transesterification of a lipid.
 4. The process accordingto claim 1, characterized in that the metal-ion forming agent is calciumchloride or magnesium chloride, preferably calcium chloride.
 5. Theprocess according to claim 1, characterized by adding the metal-ionforming agent as a solid or as a liquid, preferably as a solid.
 6. Theprocess according to claim 1, characterized by adding the metal-ionforming agent in an amount that precipitates at least 40 mol-% of thesoap of the starting material, preferably the agent is added in anamount, through which a stoichiometric amount of metal ion is formedwith regard to the amount of soap, most preferably in a stoichiometricexcess of 10 mol-%.
 7. The process according to claim 1, characterizedin that the insoluble phase comprises the soap.
 8. The process accordingto claim 1, characterized in that the liquid phase comprises thepolyhydric alcohol or the monohydric alcohol or a mixture of severalalcohols.
 9. The process according to claim 1, characterized by addingan acid into the insoluble phase, preferably hydrochloric acid orsulphuric acid, whereby a fatty acid or a mixture of fatty acids isformed.
 10. The process according to claim 1, characterized by adding amonohydric alcohol and an acid catalyst, preferably hydrochloric acid orsulphuric acid, into the insoluble phase to form a fatty acid ester. 11.The process according to claim 1, characterized by adding first an acidto the insoluble phase to form a fatty acid, and then adding amonohydric alcohol and an acid catalyst into at least a portion of theformed fatty acid to esterify the fatty acid.
 12. The process accordingto claim 10, characterized in that the molar amount of monohydricalcohol compared to the molar amount of organic matter is at least 40%,preferably an equivalent amount.
 13. The process according to claim 11,characterized in that the molar amount of monohydric alcohol compared tothe molar amount of organic matter is at least 40%, preferably anequivalent amount.
 14. The process according to claim 1, characterizedin that the organic phase comprises a fatty acid ester or a mixture offatty acid esters and the aqueous phase comprises water and mineralsalts.
 15. The process according to claim 1, characterized by separatingthe organic phase and the aqueous phase from each other and collectingthem.
 16. Use of the fatty acid or the fatty acid ester or the mixtureof fatty acids or fatty acid esters produced by the process according toclaim 1 as a feed in the esterification of fatty acids or in processes,where lipids are hydrotreated.
 17. Use of an alcohol mixture generatedin the production of biodiesel for manufacturing a fatty acid or a fattyacid ester or a mixture thereof according to the process of claim 1.